1. Field of the Invention
The present invention relates to a substrate processing method and substrate processing apparatus for processing a substrate with a coating film formed thereon, which is used for e.g., manufacturing semiconductor devices.
2. Description of the Related Art
In a photolithography step for semiconductor devices, a resist is applied onto a semiconductor wafer (which will be simply referred to as “wafer” hereinafter) to form a resist film. Then, the resist film is subjected to a light exposure process in accordance with a predetermined circuit pattern. Then, the light-exposed pattern thus formed is subjected to a developing process to form a circuit pattern on the resist film.
In a photolithography step of this type, a resist coating/developing system is used for performing a series of processes, such as resist coating, development after light exposure, and heat processes accompanying them. There is a system of this kind that includes a plurality of processing units for performing respective processes, and a transfer unit for sequentially transferring a plurality of wafers to and from the processing units in accordance with the order of processes (Jpn. Pat. Appln. KOKAI Publication No. 2003-258076).
Further, in a photolithography step, a coating liquid of, e.g., resist or BARC (anti-reflective coating) is applied, and is then baked and cured (hardened by baking) by a heat process, such as a pre-baking process. This heat process may be performed by a heat processing unit of the type that includes a heating plate configured to perform a baking process on a wafer placed thereon, while being heated by a heater (U.S. Pat. No. 5,620,560 and Jpn. Pat. Appln. KOKAI Publication No. 9-15572).
Where a pre-baking process is performed by such a heat processing unit in the system described above, a transfer unit is used for sequentially transferring a plurality of wafers to and from a plurality of processing units in accordance with the order of processes. In this case, the wafers suffer differences in, e.g., waiting time for the respective processing units, depending on the busyness of the transfer unit, so the wafers have different time lengths from the time each wafer is coated with a coating liquid to the time it is loaded into the heat processing unit. Such differences in transfer time length may bring about fluctuations in the distribution of a specific component after the coating liquid is baked and cured, although it depends on the coating liquid. It follows that the line width (CD (Critical Dimension)) may become unequal among the wafers.
Previously, fluctuates of this kind did not cause serious problems, but, in recent years, even slight fluctuates of this kind are problematic, because circuit patterns used for semiconductor devices have become drastically smaller. Accordingly, it is required to suppress the fluctuations described above in pre-baking processes.